How do you justify 5 (n + 4 ) + 9n = (5n+ 20 ) + 9n?

5(n + 4) + 9n = (5n + 20) + 9n
5*n + 5*4 + 9n = 5n + 20 + 9n
5n + 20 + 9n = 14n + 20
14n + 20 = 14n + 20
[5(n + 4) + 9n ≡ (5n + 20) + 9n] (identity)

simply use the distributive property a(x+y) = ax+ay. Therefore 5( n+4) + 9n = 1(5n+20) +9n.
5n+20 + 9n = 5n + 20 +9n.

14n + 20 = 14n + 20

first do the parenthases
which equals 5n + 20
then second you add common factors
5n + 9n = 14n
then your answer becomes 14n + 20

RULE

a (x + b) = a x + a b

THUS

5 (n + 4) = 5 n + 20

Question
5 (n + 4) + 9 n
5 n + 20 + 9 n
14 n + 20

5(n+4) expands to 5n+20???